title: Tissue distribution of dexamethasone in feline ocular structures following single topical application of dexamethasone as an ointment or suspension.
abstract: OBJECTIVE
  To compare the dexamethasone concentration in various structures of the feline eye following a single topical application of dexamethasone as an ophthalmic ointment or suspension.
  
  
  METHODS
  Nineteen cats, euthanized due to reasons not related to this study, were selected and their ocular health status evaluated. Selected animals were treated with dexamethasone ointment or suspension.
  
  
  METHODS
  The concentration of dexamethasone was determined in the following structures of the eye: third eyelid, cornea, aqueous humor, iris, lens, vitreous body, and choroid/retina. The dexamethasone concentration in the eye was measured by radioimmunoassay. The applied amount of dexamethasone was 0.05 mg in 0.05 mL Isopto Dex(®) ophthalmic suspension and 0.05 mL Isopto Dex(®) ophthalmic ointment, respectively. Cats were treated once with ointment or suspension and were euthanized 3 h or 6 h after treatment.
  
  
  RESULTS
  At 3 h after topical administration the highest concentrations of dexamethasone were measured in the anterior structures of the eye. The concentrations after application of ointment and suspension were comparable. However, 6 h after administration, the concentrations decreased after administration of suspension and increased further after administration of the ointment, leading to significantly higher concentrations of dexamethasone in the third eyelid, cornea and choroid/retina after treatment with ointment.
  
  
  CONCLUSIONS
  Therapeutically relevant concentrations of dexamethasone after a single topical administration were only achieved in the anterior structures of the eye. Six hours after application there was a substantially higher amount of dexamethasone in the anterior structures of cat eyes treated with ophthalmic ointment compared to ophthalmic suspension.
authors.affiliation: Institute for Pharmacology, Toxicology and Pharmacy, Hannover, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Bessonova
authors.forename: Andrea
authors.initials: A
authors.lastname: Meyer-Lindenberg
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bäumer
authors.forename: Manfred
authors.initials: M
authors.lastname: Kietzmann
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D002415:Cats; D003907:Dexamethasone / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D005123:Eye / Q000378:metabolism; D009824:Ointments; D013535:Suspensions; D014018:Tissue Distribution
chemical_list: D000893:Anti-Inflammatory Agents; D009824:Ointments; D013535:Suspensions; D003907:Dexamethasone